A piston rod-less drive of this type is disclosed in the German patent publication 3,509,891 A1. It possesses a housing in which a piston is arranged able to be slid by fluid power and is drivingly coupled with a power transmitting member extending through a longitudinal slot in the housing. In order to prevent escape of fluid the inner slot opening facing the piston receiving space of the longitudinal slot is provided with a sealing band. At the outer slot opening located at the outer face of the housing a covering band is provided, which extends along the length of the slot and is secured to the housing at an attachment section on the long side to a first longitudinal side of the outer slot opening. A covering section, pivotally connected with this attachment section, of the covering band covers the outer slot opening axially on either side of the power transmitting member in order to prevent the ingress of dirt into the longitudinal slot. At the power transmitting member the covering section is pivoted outward into a hatch-open position in order to permit the extension of the force coupling member through an opening with the function of a hatch. This hatch zone is displaced along the longitudinal slot in accordance with the movement and instantaneous position of the piston and of the force coupling member connected with it.
The assumption of the covering position of the covering section is in the case of the known linear drive to be ensured by a sufficient biasing effect, which automatically returns the covering section and also the correspondingly fashioned sealing band, after pivoting into the release position automatically. The biasing effect is produced by a connecting rib integrally made with the covering band and the sealing band, such rib extending through the longitudinal slot. In this case there is however the disadvantage that in the course of time material fatigue will impair reliable assumption of the covering position.
Similar problems occur with the covering band based on the same principles in accordance with the U.S. Pat. No. 4,555,980. Departing from the design in accordance with the German patent publication 3,509,891 A1 the covering means in this case however has two covering bands which jointly cover the longitudinal slot.
Admittedly there has in the said U.S. Pat. No. 4,555,980 also been a suggestion to secure the covering band by means of a releasable detent connection with the sealing band in the covering position.
However in this case a different type of covering band is provided, in the case of which the covering band has its full width moved clear of the longitudinal slot at the force coupling member, something which as regards the force coupling member demands a complicated structure, because it must be provided with a passage for the covering band to run through.